I actually enjoyed my ride along the A82 in both directions and never found the traffic to be intimidating. You Scottish wusses have no idea what heavy traffic is like. Come down to Leeds and try commuting on a bike. It's something that even I'd think twice about if the route had no cycle lanes.
Look it up, it might not be the most dangerous or busy, but it is never far away from being in reports like this, meaning that it isn't just me who thinks (long suspected more like) that it isn't exactly the safest road ever!
Now, these might be old, but a road doesn't change unless upgraded:
http://www.bbc.co.uk/news/uk-scotland-highlands-islands-14590493
I imagine the deaths are not any better:
http://news.bbc.co.uk/1/hi/scotland/7286341.stm
http://news.bbc.co.uk/1/hi/scotland/highlands_and_islands/7189168.stm
There are plenty of reports and pleas for the road to be upgraded, it is well known for being dangerous.
North of Tarbert, although the cycle track has ended here and there is no alternative route, the Tarbert to Crianlarach/Tyndrum section is regarded as being particularly bad, and, well, it isn't surprising to see why if you know it!
For those who don't, it is the section that runs beside Loch Lomond, hemmed in by one side by the Loch on one side, hills and the railway on the other, there is very little space and there is nowhere to go (there have been plans to upgrade the road and make it safer, but its difficult to do much in the space provided). Combined with the fact that it is quite narrow and windey, and with it being one of Scotland's main roads, it isn't difficult to see why it is seen as dangerous.
Put a cyclist or cyclists in the middle of that and an already clogged bit of road becomes even worse!

There is (or at was) even a section where its one way and you have to wait your turn via a set of traffic lights. A one way A road. Great!!
Maybe I am being a bit lazy, but with its reputation, I just class the whole road as being one to avoid. It is a motorway in all but name anyway (with a dangerous narrow bit in the middle), and, although it might not be the mean streets of Leeds according to Vernon, it's still no country lane, that's for sure!!